Cyclone Burner

ABSTRACT

A description is given of a cyclone burner for converting solid fuel comprising a substantially rotationally-symmetric whirling chamber ( 1 ), means for introducing gas and fuel into the whirling chamber ( 1 ), means for bringing the gas and fuel into rotation in the whirling chamber ( 1 ) and an outlet ( 4 ) for the gas and the converted fuel where the outlet ( 4 ) is centrally positioned in the outlet end ( 3 ) of the whirling chamber ( 1 ). The cyclone burner is characterized in that the whirling chamber ( 1 ) comprises a conical shaped portion ( 2 ) having the smaller diameter furthest from the outlet end ( 3 ) and in that the means ( 5 ) for introducing gas are connected to the whirling chamber ( 1 ) along the length of the conical shaped portion ( 2 ).

The present invention relates to a cyclone burner for converting solidfuel comprising a substantially rotationally-symmetric whirling chamber,means for introducing gas and fuel into the whirling chamber, means forbringing the gas and fuel into rotation in the whirling chamber and anoutlet for the gas and the converted fuel where the outlet is centrallypositioned in the outlet end of the whirling chamber.

Cyclone burners of the above-mentioned type are well known in theindustry, being used inter alia in power plants. From U.S. Pat. No.7,261,047 BB, for example, is known a horizontally positioned cycloneburner where the fuel is introduced at the back end of a cyclonechamber, whereafter it flows along with the gas stream towards a conicaloutlet end where particle separation takes place. In this type ofcyclone burner, the fuel must be substantially converted before itreaches the outlet end, otherwise the result would be build-up of fuelat this location, eventually leading to complete interruption of thefuel flow and/or its discharge by entrainment out of the chamber. Theassociated disadvantage is that the particles must be so finely dividedas to ensure almost complete conversion of the particles before theyreach the outlet end of the burner. As a result, the total amount ofretained fuel in the compartment will be at a comparatively modestlevel, therefore necessitating an unnecessary degree of comminution ofthe fuel in order to ensure an acceptable degree of conversion for agiven chamber volume. Another consequence of the design is that the fuelwill not be substantially distributed along the length of thecompartment, but instead it will accumulate at one of the ends of thechamber, entailing poor control of the temperature distribution in thechamber and leading to undesirable formation of slags.

It is an objective of the present invention to provide a cyclone burnerwhereby the aforementioned disadvantages are eliminated or significantlyreduced.

This is achieved by a cyclone burner of the kind mentioned in theintroduction and being characterized in that the whirling chambercomprises a conical shaped portion having the smaller diameter furthestfrom the outlet end and in that the means for introducing gas areconnected to the whirling chamber along the length of the conical shapedportion.

Hereby it is obtained that the gas and fuel are forcibly led along thewall of the conical shaped portion of the whirling chamber back towardsthe back end of the whirling chamber at which location they willsubsequently be led towards the eddy flow centrally in the whirlingchamber and then led to and discharged through the outlet. Hence asignificant amount of fuel can be retained, thereby reducing the needfor comminuting the fuel to a very small particle size. The angle of theconical shaped portion of the whirling chamber relative to the centreaxis of the whirling chamber will influence the effect of thecentrifugal counter force acting on the rotating fuel in the whirlingchamber. At a given gas stream and gas velocity, a large angle willallow a greater amount of fuel to be retained than achievable if asmaller angle is applied for the same gas stream and gas velocity.However, if the angle is too big the whirling chamber may lose itsself-discharging capability if excessively filled, potentially givingrise to an undesirable accumulation of the fuel. Therefore, the angle isalso important in terms of preventing accumulation of fuel. It ispreferred that the angle of the conical shaped portion is kept withinthe range of 5 to 20 degrees. The angle for optimization of operatingcharacteristics varies in dependence of quality, size and type of fuel.

Converted fuel is taken to mean fuel which has been introduced to thewhirling chamber, where the fuel has undergone combustion, pyrolysis,gasification and/or mechanical comminution due to forces of collisionand friction.

It is preferred that the predominant portion or the entire whirlingchamber is conically and that the means for introducing gas are arrangedover the whole conical shaped portion in the longitudinal direction ofthe cyclone burner. The cyclone burner may be arranged inclined,however, it is preferred that the cyclone burner is arrangedhorizontally.

The means for bringing the gas and the fuel into rotation in thewhirling chamber may in principle comprise any suitable means as long asthey are capable of bringing the gases and fuel into rotation. Forexample, the means may comprise a number of fixed devices in thewhirling chamber which are formed and positioned so that they willimpart rotation to the gas and the fuel. However, it is preferred thatthe means for introducing gas (for example air, O₂, H₂O or CO₂, mixed orpure) are connected substantially tangentially to the conical shapedportion. The means for introducing fuel may also comprise a tangentiallyarranged fuel inlet. Generally a tangential inlet, which is a commonfeature of cyclone separators, will cause an introduced medium to bebrought into rotation in the cyclone chamber when being fed hereto atsufficient velocity.

The means for introducing gas, which are connected to the whirlingchamber along the length the conical shaped portion, may in principlecomprise any suitable means as long as they are capable of introducingthe gas along the conical shaped portion. The means are preferablyarranged tangentially over at least the major part of the conical shapedportion in the longitudinal direction of the cyclone burner. For examplethe means may comprise a gas inlet with a single opening extending overthe major part of the length of the conical shaped portion. However, itis preferred that the means for introducing gas comprise a number of gasinlets, at least two, arranged one after another along the length of theconical shaped portion, preferably along the major part of the conicalshaped portion. Such tangentially inlets arranged at the conical shapedportion in the longitudinal direction of the cyclone burner combinedwith a fuel inlet connected to the half of the whirling chamber which isclosest to the outlet end, will force the fuel and gas along the wall ofthe conical shaped portion of the whirling chamber back towards the backend of the whirling chamber. During this movement the fuel will beconverted and subsequently led towards the eddy flow centrally in thewhirling chamber for being transported to and discharged through theoutlet.

It is further preferred that the end faces at each end of the whirlingchamber are plane. One or several gas nozzles may advantageously befitted to the back end face for co-firing with other fuels, such as oil,gas, coal or sawdust.

It is preferred that the outlet comprises an outlet duct which protrudesinto the whirling chamber in order to stabilize the eddy flow in thewhirling chamber.

In one embodiment the means for introducing fuel is connected to thathalf of the whirling chamber which is closest to the outlet end.

The cyclone burner may in principle be used for all types of industrialprocesses which require a source of heat like rotary kilns or powerplant boilers. For example it may be used for manufacturing cementclinker where cement raw materials are introduced to a cement or mineralprocessing plant where raw materials are supplied with thermal energyand converted into cement clinker or other mineral products, e.g. burnedlime. Here a cyclone burner may at least provide some of the thermalenergy. If the cyclone burner is used for processing materials in arotary kiln, its outlet may be fitted to a burner lance extending intothe rotary kiln, thereby allowing the converted fuel to be fed andignited at a distance further inside the rotary kiln. With this type ofarrangement, it will be possible to use heated process gases, e.g. froma clinker cooler, for the gas inlets connected to the whirling chamber.

The invention will now be explained in further details with reference tothe drawing, being diagrammatical, and where

FIG. 1 a and FIG. 1 b show a cross-sectional view and a view from theoutlet end, respectively, of a cyclone burner according to theinvention, and

FIG. 2 shows a cross-sectional view of another embodiment of a cycloneburner according to the invention.

In FIG. 1 a and FIG. 1 b are shown a cyclone burner for converting solidfuel. The cyclone burner is arranged horizontally and comprises aconical shaped portion 2, which makes up the whirling chamber 1, havingthe smaller diameter furthest from the outlet end 3 and terminated witha plane back end face 7. An outlet 4 for the gas and the converted fuelis centrally positioned in the outlet end 3 of the whirling chamber 1. Afuel inlet 6 is connected tangentially to the whirling chamber 1 closeto the outlet end 3. Furthermore a number of tangentially arranged gasinlets 5 a for introducing gas and for bringing the gas and the fuelinto rotation in the whirling chamber 1 are arranged one after anotheralong the whole length of the conical wall. In this way the gas and thefine fuel particles are forcibly led along the conical wall towards theback end face 7 of the whirling chamber 1 where they will be led towardsthe eddy flow centrally in the whirling chamber 1 and then led to anddischarged through the outlet 4, whereas the larger particles will beled towards the larger diameter end, hence a significant amount of fuelcan be retained, thereby reducing the need for comminuting the fuel to avery small particle size. The angle of the conical wall in the whirlingchamber 1 relative to the centre axis of the chamber will influence theeffect of the centrifugal counter force acting on the rotating fuel inthe whirling chamber 1. It is preferred that the angle of the conicalshaped portion relative to the centre axis 8 of the whirling chamber isbetween of 5 and 20 degrees. The angle for optimization of operatingcharacteristics varies in dependence of quality, size and type of fuel.The whirling chamber 1 is heated by use of oil, gas or other medium toat least 550° C. so as to ensure self-ignition and conversion of thesolid fuel which is introduced through the fuel inlet 6. When switchingfrom oil/gas to solid fuel, the gas/fuel ratio is kept at anover-stoichiometric or near-stoichiometric level to ensure effectiveignition and additional heating. Once the target operating temperaturehas been reached, the fuel rate is increased so that the whirlingchamber 1 will have the exact capability to convert all the input fuelto gas. This is achieved at a temperature of around 900-1100° C. and ata gas/fuel ratio of around 20-40% (air deficit) of the stoichiometriclevel necessary for complete combustion. The aim is to operate at thelowest possible temperature and at a minimum air/fuel ratio, which isachieved by increasing the volume of fuel particles so that it will beslightly higher than the volume which can be converted in the whirlingchamber 1. Hence the rotating amount of particles is gradually increasedand more and more particles will be forcibly led towards the smaller endof the conical whirling chamber 1, while, at the same time, theparticles at this location will be moving closer to the centre of thewhirling chamber 1. The particles rotate at increased angular velocitywhen moving with the gas towards the gradually diminished radius of thecone. Because of the increased centrifugal force thereby generated andthe out flowing gas stream the particles separate in such a way that thelarge particles will remain near the large conical end of the whirlingchamber 1 while the small particles are simultaneously entrained in thegas stream moving towards the small conical end of the whirling chamber1. At some point in time, the accumulation of the small particles willreach an extent where their rotation are reduced and some of theparticles will “drop” out into the central gas stream which isdischarged through the outlet 4. The particles which are most easilyentrained in the outgoing gas stream will be those having a relativelylarge surface relative to mass, i.e. the smallest and lightest fuelparticles, whereas any large/heavy particles will to a certain extenthave a tendency to drop out of the gas stream and back into the rotatingparticle mass. The now continuously separated stream of fine particleswill restore the balance in the whirling chamber 1, whereby the volumeof retained particles will find an equilibrium position. The separatedparticles are burnt out together with the gas in the subsequent flame.The overall aim is to ensure that the gas/fuel ratio is adjusted exactlyso that the particles will have time to burn out sufficiently in thesubsequent flame. In order to maintain full circulation of the entireparticle mass, the gas (air or other gases) is introduced through thegas inlets 5 a with a high tangential velocity in the whirling chamber1. Regulation of gas volume and velocity is achieved by adapting thearea in the gas inlets 5 a and the air pressure ahead of the gas inlets5 a. The adapting may also be achieved by having a number of gas inlets5 a fully opened while keeping the remaining gas inlets 5 a closed. Thegas inlets 5 a may be arranged in one or more rows in the longitudinaldirection of the conical wall of the whirling chamber 1. Furthermore anumber of gas inlets 5 b (one gas inlet 5 b is shown with dotted linesin FIG. 1 b) may be connected to the whirling chamber 1 in locationsalong the length of the conical shaped portion 2 and being offset fromeach other both in the circumferential direction and in the longitudinaldirection.

In FIG. 2 is shown an embodiment of a cyclone burner similar to the onein FIG. 1 except for the arrangement for introducing the gas into thewhirling chamber 1. The gas inlet 5 c has a single opening extendingover the major part of the conical wall in the whirling chamber 1whereby only one gas inlet 5 c is needed for introduction of gas as itwill affect the whole length of which it extents. The gas inlet 5 c maycomprise means for adjusting the opening area through which the gasflows.

1. A cyclone burner for converting solid fuel comprising a substantiallyrotationally-symmetric whirling chamber (1), means (5, 6) forintroducing gas and fuel into the whirling chamber (1), means forbringing the gas and fuel into rotation in the whirling chamber (1) andan outlet (4) for the gas and the converted fuel where the outlet (4) iscentrally positioned in the outlet end (3) of the whirling chamber (1)characterized in that the whirling chamber (1) comprises a conicalshaped portion (2) having the smaller diameter furthest from the outletend (3) and in that the means (5) for introducing gas are connected tothe whirling chamber (1) along the length of the conical shaped portion(2).
 2. A cyclone burner according to claim 1 characterized in that themeans (5) for introducing gas are connected tangentially to the conicalshaped portion (2).
 3. A cyclone burner according to claim 1 or 2characterized in that the means for introducing gas comprise a number ofgas inlets (5 a) arranged one after another along the length of theconical shaped portion (2).
 4. A cyclone burner according to claim 1 or2 characterized in that the means for introducing gas comprise a gasinlet (5 c) with a single opening extending over the major part of thelength of the conical shaped portion (2).
 5. A cyclone burner accordingto any preceding claim characterized in that the means for introducingfuel comprise a tangentially arranged fuel inlet (6).
 6. A cycloneburner according to any preceding claim characterized in that the angleof the conical shaped portion (2) relative to the centre axis (8) of thewhirling chamber (1) is between of 5 and 20 degrees.
 7. A cyclone burneraccording to any preceding claim characterized in that the predominantportion or the entire whirling chamber (1) is conically.
 8. A cycloneburner according to any preceding claim characterized in that thecyclone burner is arranged horizontally.
 9. A cyclone burner accordingto any preceding claim characterized in that the outlet (4) comprises anoutlet duct which protrudes into the whirling chamber (1).
 10. A cycloneburner according to any preceding claim characterized in that the means(6) for introducing fuel is connected to that half of the whirlingchamber (1) which is closest to the outlet end (3).